Practical lesson of Photosynthesis: A demonstration of Hill reaction in chloroplasts with energy dissipation by fluorescence upon photosystems uncoupling or inhibition by Diuron herbicide

• Main Author: Vadim Ravara Viviani
• Format: Article
• Language: Portuguese
• Published: Sociedade Brasileira de Bioquímica e Biologia Molecular, SBBq 2016-05-01
• Series: Journal of Biochemistry Education
• Subjects: Fotossíntese; estados excitados, fluorescência
• Online Access: http://bioquimica.org.br/revista/ojs/index.php/REB/article/view/557

During photosynthesis, the photochemical electron transfer process is easily demonstrated by the Hill reaction, where artificial electron acceptors are reduced by active chloroplasts suspensions in the presence of light.  However, the destiny of luminous energy absorbed by chlorophyll molecules in uncoupled or damaged photosystems is not usually demonstrated. Here we provide an adaptation of the classical Hill reaction using intact spinach chloroplasts, which includes the visualization of energy dissipation by fluorescence in lysed chloroplasts, and a dose/effect response in photosystems inhibited by the herbicide DCMU. This laboratory lesson, which is aimed to biochemistry and biophysics for undergraduate courses of Chemistry, Biological, Environmental and Agricultural Sciences, provides the basic photochemical principles using the classical Hill reaction, and photophysical principles through the visualization of energy dissipation by chlorophyll fluorescence,  improving the understanding of the photosynthetic process, and introducing the concept of fluorescence and its applications as bioanalytical tool to monitor photosynthesis in plants and vegetal ecosystems.